Vibrations emitted from rotating components included with gas turbine engines can reduce passenger comfort and degrade various aspects of engine performance, including thrust output and fuel efficiency. Additionally, rotating components can experience excessive vibrations when rotated at specific speeds that align with rotor system flexible mode frequencies, possibly resulting in degraded system performance or damage to components. It is thus desirable to damp such vibrations prior to transmission to the aircraft fuselage and, preferably, prior to transmission to the engine's static infrastructure or housing. It is also desirable to damp vibrations to limit the response at rotor system flexible mode frequencies to maximize system performance and avoid potential damage to the system. For these reasons, modern gas turbine engine are commonly equipped with squeeze film dampers (“SFDs”), which are mounted around one or more of the rotor bearings to reduce the response at rotor system flexible modes, as well as to reduce transmission of vibrations to the engine housing. A squeeze film damper typically includes an inner journal and an damper outer housing, which are affixed to the rotor bearing and to the engine housing, respectively. The inner circumferential surface of the journal is radially spaced from outer circumferential surface of the damper housing to define an annulus, which is filled with a damping fluid. In the normal or design position, the journal and the damper housing are generally concentric and the width of the annulus is constant. However, during engine operation, the journal moves in conjunction with the rotor bearing relative to the damper housing and the static engine infrastructure. As the journal moves between different eccentric positions along an orbital or whirl-type motion path, the geometry of the annulus changes. Damping fluid is continually displaced by the dimensional changes in the damping fluid annulus, and the transmission of vibrations through the SFD and to the engine housing are damped by viscous losses and fluid shearing.
SFDs provide vibration attenuation in a relatively compact and lightweight package well-suited for deployment within a gas turbine engine. SFDs are, however, limited in several respects. First, SFDs are active hydraulic devices requiring lubricant supplies and plumbing, which adds undesired part count, complexity, and cost to the gas turbine engine. Second, the stiffness and damping profiles of an SFD are highly non-linear and difficult to predict. Thus, while a given SFD can be tuned to provide peak damping at a frequency corresponding to a targeted engine critical mode, the SFD will provide less-than-optimal damping at other operational frequencies and engine critical modes. Furthermore, as the engine critical modes vary in conjunction with changing rotor imbalances, SFDs may gradually become less effective at attenuating vibrations over the operational lifespan of a gas turbine engine. As a further limitation, the stiffness and damping profiles of an SFD are inherently linked and cannot be independently tuned. As a result, it can be difficult to optimize the damping characteristics of an SFD without reducing stiffness and sacrificing some degree of rotor centerline control. Poor centerline control decreases the ability of the SFD to counteract static loading conditions (e.g., gravity sag or maneuver loads) and generally requires the provision of larger tip clearances within the gas turbine engine, which reduces overall engine efficiency. Moderate improvements in the linearity of the SFD damping and stiffness profiles can be realized through the addition of a centering spring; however, spring-centered SFDs still provide less-than-ideal stiffness and damping profiles and remain limited by the other drawbacks noted above.
There thus exists an ongoing need to provide embodiments of a bearing support damper suitable for usage within gas turbine engine and other turbomachinery that overcomes most, if not all, of the above-noted limitations. In particular, it would be desirable to provide a bearing support damper that provides substantially linear stiffness and damping profiles over a relatively broad frequency and amplitude ranges, and that does not require an active lubricant supply. Ideally, embodiments of such a bearing support damper would have a highly compact envelope to facilitate incorporation of the bearing support damper into existing gas turbine engine platforms. It would also be desirable to provide embodiments of a gas turbine engine including such a bearing support damper, as well as methods for the manufacture of a bearing support damper. Other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying drawings and the foregoing Background.